The present teachings enable communication operations between a terminal and a LEO constellation in presence of line-of-sight blockage for part of the sky, so long as satellites are available in other unblocked parts.
Prior art communication systems based on a Low Earth Orbit (LEO) LEO constellation that used only one unidirectional antenna, mounted the antenna high enough that there was no blockage between a terminal and an ephemeris of a satellite in the LEO constellation. Other alternatives required more antennas and less efficient use of satellite bandwidth.
Prior art communication systems also precluded usage of K-Band (Ka-band or Ku-band) for LEO constellations. Traditionally, Ku-band and Ka-band have been used for Fixed Satellite Systems (FSS) using geosynchronous (GEO) satellites. This enables selection of an antenna site with a clear view of the GEO satellite, generally, southerly in the Northern hemisphere. As the GEO satellite appears to be in a fixed location at installation, an antenna is installed such that blockages, such as, buildings, trees or the like, are not in a line of site of the GEO satellite and thus the blockages are of no consequence. Other prior art LEO systems (and MOBILESAT GEO systems), such as IRIDIUM, GLOBALSTAR, THURAYA and others have been designed with L-Band and S-Band user links, that are usable with Omni-directional antennas. For the terminals to look for channels, they only need to look for frequencies and blockage geometry is not an issue. In such systems, there are several satellites in the field of view of the omnidirectional antenna. Even though a path to a satellite in the constellation is blocked, paths to other satellites that are differentiated by frequency in the constellation are available. As such, the terminal can determine which satellites in the constellation are available without any antenna motion. Other prior art systems, such as, GLOBALSTAR, even allow for diversity, where multiple satellite paths are used for communication simultaneously.